Okay so I had absolutely terrible battery on the s21 ultra out of the box.
I followed some advice I got elsewhere, and did 2 things that have made a big difference.
1.Reset the phone back to factory settings, and do a fresh install without smart switch. This took some work to do, but ultimately allowed me to cut out about 150 apps I have been transferring around without using them in years.
2.With the apps remaining I went into the battery section, and manually added every app I do not want notifications from to the deep sleep category.
Between these 2 steps I went from 4 hours SOT to close to 7.5 today with some in the tank.